1. Field of the Invention
This invention relates to an osmotically driven active agent dispenser.
2. Description of the Prior Art
The invention is a modification of the osmotically driven active agent dispenser disclosed in U.S. Pat. No. 3,916,899. Briefly, the patented dispenser comprises: a core of an osmotically effective active agent composition; a water insoluble wall that is impermeable to the composition, has a controlled permeability to water and encloses the core; and one or more particularly sized passageways extending through the wall to the core. When placed in an aqueous environment, such as the gastrointestinal tract, eye, vagina, and uterus, water is imbibed from the environment by the composition through the wall causing the composition to be dissolved, a pressure gradient between the interior and exterior of the dispenser to be generated, and the dissolved composition to be pumped out the passageway(s) into the environment. The release of active agent from these dispensers is continuous, sustained, predetermined, and substantially constant over a major portion of the release period. The patent discloses that the passageways in the wall may be formed mechanically, such as by drilling, or in situ by erosion of a bioerodible component incorporated into the wall.
Commonly owned U.S. application Ser. No. 578,979 filed May 19, 1975 discloses a drug dispenser in the form of a unit body of a mixture of discrete particulate depots of an osmotically effective drug composition dispersed in a water insoluble, water permeable polymer. The depots imbibe water from the environment serially beginning with those nearest the exposed surface of the body until enough pressure is generated within the depots to cause them to burst open. As the depots burst open the drug composition within them is released.
U.S. Pat. No. 2,478,182 describes salt tablets comprised of compressed salt granules coated with cellulose acetate or cellulose nitrate. According to the patent the cellulose derivative penetrates the compressed granules to form a honeycomb structure. Upon ingestion of the tablets, water dialyzes into the compartments of the honeycomb and salt dialyzes out. The patent also says the honeycomb compartments burst when they become engorged with water.
U.S. Pat. No. 3,247,066 describes medicinal beads that burst to release medicine. The beads consist of a core of a water swellable colloid containig a drug that is coated with a polymer that is water permeable and inert to gastrointestinal fluids. When the beads are ingested, water diffuses inwardly through the coating to swell the colloid core. This swelling creates sufficient pressure to burst the coating, whereby the entire quantity of drug in the core is released.
Also, the agricultural chemical art literature describes various slow release formulations of fertilizer or pesticide and polymer. For instance, U.S. Pat. No. 3,708,276 describes grains of fertilizer that are coated with water insoluble resins containing foreign particles. The presence of such particles is said to affect the permeability and the rate at which the fertilizer is eluted.